Electron tube construction



Nov. 13, 1934. E. Ko'cH 1,980,805

ELECTRON TUBE CONSTRUCTION Filed May 22, 1951 -2 Sheets-Sheet' 1 FM'YZTFE EFZZI Z1 01:22.

NOV. 13, 1934. H 7 1,980,805

ELECTRON TUBE CONSTRUCTION Filed May 22, 1951 2 Sheets-Shet 2 H IIJFK/517217.77 Ma y Ear/[7.52755 Patented Nov. 13, 1934 PATENT OFFICE1,980,805 ELECTRON TUBE CONSTRUCTION Earl L. Koch, Chicago, 111.,assignor, by mcsne assignments, to Earl L. Koch Holding Corporation, NewYork, N. Y., a corporation of New York Application May 22, 1931, SerialNo. 539,184

5 Claims.

This invention relates to improvementsin electron tube construction asapplied more particularly to power tubes or thermionic generators suchas are used for transmitting in radio broadcasting and radio telegraphy.

This invention has for one of its objects the provision of a new andimproved arrangement of parts in a four element tube for eliminatingfeed-back through electrostatic coupling between the active grid elementand the anode element of the tube. a

In transmitting systems of the high frequency type, it is essential thatthe capacity between the active grid element and the anode element dueto coupling between these two elements be kept as low as possible, andit is to secure this end that this invention has been designed.

Another object of the invention is the provision of a shield or screengrid element which is disposed between the anode element and the activegrid element of the tube; the active grid element being affixed at bothends to a suitable support; the shield or screen grid element beingsimilarly mounted. The screen grid element completely surrounds theactive grid element and fully shields the active grid element and itssupport from the anode element, to reduce the feedback through capacitycoupling between the active grid element and the anode element to aminimum.

This method of mounting the elements also permits the terminal conductorof the active grid element to be placed at one end of the glass envelopeof the tube to isolate it from the terminal conductors of the screengrid and filament; which are at the opposite end of the glass envelope;to prevent coupling from this source.

Further objects and advantages of the invention are set forth in theensuing description, and several embodiments of the invention areillustrated in the accompanying drawings; but the disclosure isexplanatory only, and the construction actually shown may be varied, asby altering the shape, size and arrangement of the parts,

without going beyond the principle of the invention or exceeding thescope of the appended claims.

On said drawings:

Figure 1 shows in section one form of tube according to the invention;and

Figure 2 is a similar View of another form.

The same numerals identify the same parts throughout.

Referring now more in detail to the invention as illustrated first inFigure 1, a tube is shown which comprises a container 1, with reentrantglass stems 2 and 3 at the opposite ends forming supports for theelements of the tube. An annular band 4 secured to the stem 2 and asimilar band 5 secured to the stem 3 are joined by rods 6, the ends ofwhich extend through loops '1 integral with the bands 4 and 5; and therods are made fast in the loops 7 preferably by spot- Welding. Theconnecting rods 6 carry suitable wire helices 8 through the turns ofwhich a screen 5 grid element in the form of a helix 9 is threaded. Thehelices 3 thus constitute supports for the screen grid helix, andmaintain the individual turns of the screen grid 9 spaced suitableintervals apart.

The stem 2 is provided with a reduced extension 10 which has securedthereto an annular band 11. Rods 12 are provided, the ends of whichextend through integral loops 13 on the band 11 andthe rods 12 aresecured in the loops 13 as before by spot-welding. The other ends of therods 12 terminate in a metallic disc 14 and are secured thereto in anysuitable manner such as by brazing or welding.

Aconducting member 15 having one end sev cured to the disc 14 and itsother end brazed to a thimble 16 of metal, which is in turn sealed inthe reduced extension 17 of the stem 3, maintains the disc 14 in centralposition relative to the screen grid 9. The rods 12 also are wound 35with suitable wire helices 18 through which a wire forming the activegrid element 19 is threaded;

and the helices 18 provide support for the active grid element 19 andkeep the individual turns of the grid 19 separated a desired distanceapart.

The annular bands 20 which surround the extensions l0 and 17 are alsoprovided with integral loops 21 through which the rods 6 also extend;and the annular bands 22, between the band 11 and the disc 14 areprovided with inte- 5 gral loops 23 through which the rods 12 extend.These give added rigidity to the screen grid and active grid elements.

The filament 24' is in the form of a U-shaped member of suitableelectron-emitting material, the ends of which are attached to theconductors 25 and 26 which lead out through the ,stem 2. The other endsof the conductors 25 and 26 are brazed to metal sleeves or thimbles 27and 28 which are sealed in the ends of a pair of projections or bosses29 and 30 integral with a glass stem 31inside the stem 2 and fusedthereto. Spacers 45 of suitable insulating material are provided withorifices through which the conductors 25 and 26 extend to hold the saidconductors apart.

Conductors 32 and 33 secured to the thimbles 27 and 28 form the externalterminals for the filament 24. The looped end 34 of the filament 24passes under the hooked end 35 of shock absorbing member 36, and a rod37 of quartz or other suitable insulating material is secured to themetallic disc 14,its other end carrying the member 36. The intermediateportion of the member36 is in the form of a coil spring 38 adapted topull the filament 24 taut.

The anode or plate 39 is in the form of a copper tube or sleeve havingsealed to its respective ends the glass envelopes 40 and 41; which bearthe internal stems 2 and 3; and, with the anode 39, make up thecontainer 1. The screen grid element 9, the active grid element 19 andthe filament 24 are mounted between the end stems 2 and 3 to form astructural unit which is easy to assemble in the container andfacilitates alignment with the tubular anode 39.

The structural unit comprising stems 2 and 3, the grids 9 and 19 andfilament 24, is inserted in the open end of the envelope 40; and, afterthe centering of the unit relative to the tubular element 39, the stems2 and 3 are 'fused orsealed in the ends of the respective glassenvelopes or sleeves 40 and 41. The remaining ends of the envelopes arethen sealed to the opposite extremities of the anode 39. A lead inconductor 42 is suitably secured to the screen grid structure 19 andbrought out through the stem 2 by a suitable seal 43. A conductor 44affixed to the sealed-in thimble 16 provides means for connecting theactive grid 19 to the external circuit.

To carry away the heat energy dissipated by the anode 39 water coolingis resorted to, and a water jacket 46 is placed around the tubular anode39. Clamping rings 4'7 and 48 and nuts 49, having threaded engagementwith the protruding ends of studs 50 and 51 in the ends of the waterjacket 46, and flanges or collars 52 afiixed to the tubular anodeelement 39 secure the water jacket 46 to the element 39. Rubber gaskets53 placed between the clamping rings 47 and 48 and the respectiveflanges of the water jacket 46 and the flanges 52 of the element 39 sealthe same against leakage. Suitable openings in the wall of the jacket 46serve as an inlet and outlet for the water or like cooling mediumfiowing in the jacket 46.

The double support for certain elements of the tube permits the shieldor screen grid element 9 which is mounted on the connecting rods 6 to bemade sufficiently long to envelope fully the active grid element 19 andthe rods 12; and hold the element 9 in concentric relation to the-activegrid element 19 and the tubular anode element 39.

The stem 15, which acts as a support for the active grid element 19,also serves to connect the active grid 19 to the external conductor 44at the end opposite that of the lead-in connections 32 and 33 of thefilament 24 and 42 of the screen grid element 19. With the active gridelement 19 thus completely surrounded by the screen grid element 9, thegrid element 19 will be efiectively shielded from the anode element 39and the feedback through capacity coupling between the active gridelement 19 and the anode element 39 is reduced to a minimum, as isessential in a power tube used with a high frequency system.

In Figure 2, a four element tube of similar but simpler construction isshown without a coolcarry clamping rings 4 and 5, and rods 6 connectthese rings and constitute a support for the screen grid 19. The rodsare secured in loops '7 on the rings 4 and 5.

The stems 2 and 3 have the reduced portions 10 and 17 to which clampingrings 11 and 11a respectively are secured and connecting rods 12 arefastened to these rings by similar loops 13. The rings 20, similarlysecured to the rods 6 serve to rigidly hold the rods '6 and preventtwisting. The bands 22 secured to the rods 12 are for the same purpose.

The filament 24, which is a loop of suitable material, is engaged at itslooped end by the flexible spring member 38, which is in turn secured byan anchor rod 15a to the reduced end of the stem 3. The ends 24a and 24bof the filament extend up through projections 29a and 30a on the stem 2in the form of leads 25 and 26.

The envelope of the electrode elements comprises an intermediate portionwhich is in the form of a copper tube or anode 39-and glass sections 40and 41 sealed to the ends of the copper tube 39. The electrodes andglass stems as a unit are inserted into one end of the tube, and when inposition can be centered in the copper anode 39 through which itextends. Thenthe respective stems 2 and 3 may be sealed to therespective glass sections 40 and 41 as in the first instance.

It is essential that the electrodes be held rigidly and in constantspaced relation, as any slight displacement of the electrodes while thetube is operating will cause frequency changes which are detrimental toperfect operation. The grid elements 9 and 19 are held by the helices 8and 18 on the connecting rods 6 and 12; which are in turn securedrespectively to the stems 2 and 3 to provide means to prevent anyrelative displacement of the grid elements 9 and 19. The filament 24being secured at its ends as before is quite stationary, and thus a tubeis provided which is most constant and efiicient in its operation. Theleads to the grids 9 and 19 are shown at 42 and 44a respectively. p

In the usual tube of this class, the elements are mounted on a stem byrods which terminate in an insulating disc for additional rigidity. Thisconstruction has its drawbacks, as possible arcing will break down theinsulation, producing gases which will greatly reduce the efficiency ofthe tube. With the improved tube herein described this risk is entirelyeliminated.

Even with the use of an insulating member to connect the elementstogether at the free ends, it is difiicult to maintain the positions ofthe elements, especially in four element tubes. The use of insulatingspacers is out of the question in high power tubes, thereby making itstill more difficult to obtain rigidity of the parts. With the doublesupport at each end absolute mechanical rigidity is afforded withoutdanger of voltage breakdown between elements due to inadequateinsulation, as all elements are afiixed to the glass stems with ampleclearances between them.

What is claimed is:

1. A thermionic tube including a container, a filament therein, means atone end of the container forming a support for the filament, atensioning device for the filament, a disc, a rod mounting the disc inthe opposite end of the container, and an insulating stem rigid withsaid disc bearing said device.

2. In a thermionic tube a hollow anode, insulating sections aflixed tothe ends of the anode,

said sectionseach having an internal stem, rods carrying a screen gridrigidly secured at their ends to each of said stems, a disc mounted onone of said stems and spaced therefrom, and a second set of rodsenveloped by the screen grid rigidly secured to the disc and the otherstem to carry a control grid in the tube.

3. A thermionic tube comprising a tubular anode, insulating sections atboth ends of said anode, each section having an inside stem with areduced extension, bands encircling both stems, rods rigidly attached tosaid bands for carrying a screen grid structure, stiffening bands onsaid rods, bands on the extensions, rods shorter than the first rodsattached rigidly to the last-named bands, stiffening bands on theshorter rods, a control grid attached to the shorter rods, and. afilament having conductors passing through one of the sections andyieldably attached to the opposite section, said filament beingsupported substantially in the center of said control grid.

4. A thermionic tube having a tubular anode,

an insulating section secured to both ends of the anode, each sectionhaving an internal stem with an extension, a disc rigid with oneextension, a band affixed to the other extension, rods attached to saiddisc and said other extension, a control grid mounted on said rods,stiifening bands engaging said rods, a filament mounted between saiddisc and said other extension, bands on the stems between saidextensions and the outer extremities of said sections, rods affixed tosaid last-named bands, a screen grid on the lastnamed rods andstiffening bands for the lastnamed rods.

5. A thermionic tube having a disc adjacent one end within the tube,rods aflixed to said disc and to the other end of the tube adapted tomount a grid, an insulating stem aifixed to said disc, a filament withinthe tube, and resilient means on said stem engaging the filament.

EARL L. KOCH.

